DS2105 MAXIM | Alldatasheet
Document overview
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Technical content
FEATURES
- Fully compliant with SCSI–1, Fast SCSI and Ultra SCSI
- Functionally compatible to the DS21S07A, targeted for high volume applications
- Provides active termination for nine signal lines
- Laser–trimmed 110 ohm termination resistors have 5% tolerance
- Low dropout voltage
- Power–down mode isolates termination resistors from the bus
- Fully supports actively negated SCSI signals
- Onboard thermal shutdown circuitry
- 16–pin plastic SOIC (DS2105) PIN ASSIGNMENT 8 9 DS2105Z 16–PIN SOIC (150 MIL) TERMPWR1 VREF1 GND PD VREF2 NC TERMPWR2 8 9 DS2105S 16–PIN SOIC (300 MIL) TERMPWR1 VREF1 GND PD VREF2 NC TERMPWR2
DESCRIPTION
Fast SCSI and Ultra SCSI require the use of active ter- minations at both ends of every cable segment in a SCSI system with single–ended drivers and receivers. The DS2105 SCSI Terminator, which is fully compliant with these standards, enables the designer to gain the benefits of active termination: greater immunity to volt- age drops on the TERMPWR (TERMination PoWeR) line, enhanced high–level noise immunity, intrinsic TERMPWR decoupling, and very low quiescent current consumption. The DS2105, which integrates a regula- tor and nine precise switched 110 ohm termination re- sistors into a monolithic IC, is a functionally compatible version of the DS21S07A. With relaxed output current and termination tolerances, the DS2105 is intended for high volume applications which require active termina- tion but not the high performance of the DS21S07A. The DS2105 is offered in both 300 mil and 150 mil SOIC packages.
The DS2105 consists of a bandgap reference, buffer amplifier, and nine termination resistors (Figure 1). The bandgap reference circuit produces a precise 2.55V level which is fed to a buffer amplifier. The buffer pro- duces a 2.85V level and is capable of sourcing at least 24 mA into each of the termination resistors when the signal line is low (active). When the driver for a given signal line turns off, the terminator will pull the signal line to 2.85V (quiescent state). To handle actively negated SCSI signals, the buffer can sink 200 mA, and VREF will move less than 60 mV. When all lines settle in the quies- cent state, the regulator will consume about 5 mA. When the DS2105 is put into power–down mode by bringing PD low, the power–down circuitry will turn off the transistors on each signal line. This will isolate the DS2105 from the signal lines and effectively remove it from the circuit. The power–down pin (PD) has an inter- nal 50KΩ pull–up resistor. To place the DS2105 into an active state, the PD pin should be left open circuited. To ensure proper operation, both the TERMPWR1 and TERMPWR2 pins must be connected to the SCSI bus TERMPWR line and both the VREF1 and VREF2 pins must be tied together externally. Each DS2105 requires a 4.7 µF capacitor connected between the VREF pins and ground. Figure 2 details a typical SCSI bus configu- ration. In an 8–bit wide SCSI bus arrangement (“A” Cable), two DS2105’s would be needed at each end of the SCSI cable in order to terminate the 18 active signal lines. In a 16–bit wide SCSI bus arrangement (“P” Cable), three DS2105’s would be needed at each end of the SCSI cable in order to terminate the 27 active signal lines. DS2105 BLOCK DIAGRAM Figure 1 GND TERMPWR1 TERMPWR2 PD POWER DOWN CIRCUITRY 50K ohm BANDGAP REFERENCE 110 ohms VREF1 VREF2 110 ohms 110 ohms 110 ohms 110 ohms 110 ohms 110 ohms 110 ohms 110 ohms
TYPICAL SCSI BUS CONFIGURATION Figure 2 Termination Power Line SCSI BUS TRANSCEIVER SCSI BUS TRANSCEIVER SCSI BUS TRANSCEIVER SCSI BUS TRANSCEIVER DS2105 TERMPWR1 TERMPWR2 VREF1 VREF2 GND R1 R2 R9 DS2105 TERMPWR1 TERMPWR2 VREF1 VREF2 GND R1 R9 SCSI CABLE C1 + C1 + NOTES: 1. C1 = 4.7 µF tantalum C2 = 2.2 µF tantalum or 4.7 µF aluminum 2. If the DS2105 is to be embedded into a peripheral that will act as a target on a SCSI bus, it is recommended that TERMPWR be derived from the SCSI cable, not generated locally. In this configuration, if a power failure occurs in the peripheral, it will not affect the bus. 3. A high frequency bypass capacitor (0.1 µF recommended) can be added in parallel to C1 for applications using fast rise/fall time drivers.
1 1 TERMPWR1 Termination Power 1. Should be connected to the SCSI TERMPWR line. Must be decoupled with either a 2.2 µF or 4.7 µF. See Figure 2. 2 2 R1 Signal Termination 1. 110 ohm termination. 3 3 R2 Signal Termination 2. 110 ohm termination. 4 4 R3 Signal Termination 3. 110 ohm termination. 5 5 R4 Signal Termination 4. 110 ohm termination. 6 6 R5 Signal Termination 5. 110 ohm termination. 7 7 VREF1 Reference Voltage 1. Must be externally connected directly to the VREF2 pin. Must be decoupled with a 4.7 µF capacitor as shown in Figure 2. 8 8 GND Ground. Signal ground; 0.0V. 9 9 TERMPWR2 Termination Power 2. Should be connected to the SCSI TERMPWR line. Must be decoupled with either a 2.2 µF or 4.7 µF. See Figure 2. 10 11 R6 Signal Termination 6. 110 ohm termination. 11 12 R7 Signal Termination 7. 110 ohm termination. 12 13 R8 Signal Termination 8. 110 ohm termination. 13 14 R9 Signal Termination 9. 110 ohm termination. 15 15 VREF2 Reference Voltage 2. Must be externally connected directly to the VREF1 pin. Must be decoupled with a 4.7 µF capacitor as shown in Figure 2. 16 16 PD Power Down. When tied low, the DS2105 enters a power–down mode. Contains an internal 50K pull–up. Strap low to deactivate the DS2105, leave open circuited to activate the DS2105. 14 10 NC No Connect. Do not connect any signal to this pin.
ABSOLUTE MAXIMUM RATINGS* Voltage on Any Pin Relative to Ground –1.0V to +7.0V Operating Temperature 0 °C to 70°C Storage Temperature –55 °C to +125°C Soldering Temperature 260 °C for 10 seconds * This is a stress rating only and functional operation of the device at these or any other conditions above those indicated in the operation sections of this specification is not implied. Exposure to absolute maximum rating conditions for extended periods of time may affect reliability. RECOMMENDED OPERATING CONDITIONS (0°C to 70°C) PARAMETER SYMBOL MIN TYP MAX UNITS NOTES TERMPWR Voltage VTP 4.00 5.25 V PD Active VPDA –0.3 +0.8 V PD Inactive VPDI 2.0 VTP +0.3 V DC CHARACTERISTICS (0°C to 70°C) PARAMETER SYMBOL MIN TYP MAX UNITS NOTES TERMPWR Current ITP ITP 5 250 mA mA 1, 3 1, 4 Power Down Current IPD 500 µA 1, 2, 5 Termination Resistance R TERM 110 118 ohm 1, 2 Die Thermal Shutdown TSD 150 °C 1 Power Down Termination Capacitance C PD 3.0 5.0 pF 1, 2, 5, 6 Input Leakage High IIH –1.0 µA 1, 8 Input Leakage Low IIL 1.0 µA 1, 7 REGULATOR CHARACTERISTICS (0°C to 70°C) PARAMETER SYMBOL MIN TYP MAX UNITS NOTES Output Voltage VREF 2.7 2.85 3.0 V 1, 2 Drop Out Voltage VDROP 0.75 1.0 V 3, 6 Output Current IOUT 24.0 mA 9 Line Regulation LIREG 1.0 2.0 % 1, 4 Load Regulation LO REG 1.3 3.0 % 1, 2 Current Limit ILIM 350 mA 1 Sink Current ISINK 200 mA 1 NOTES: 1. 4.00V < TERMPWR < 5.25V. 2. 0.0V < signal lines < 3.0V. 3. All signal lines = 0.0V. 4. All signal lines open. 5. PD = 0.0V.
- Guaranteed by design; not production tested. 7. R1 through R9 only. 8. R1 through R9 and PD. 9. VSIGNAL =0.2V. DS2105Z SCSI TERMINATOR 16–PIN SOIC (150 MIL) ÎÎ ÎÎ PKG 16–PIN DIM MIN MAX A IN. MM 0.053 1.35 0.069 1.75 A1 IN. MM 0.004 0.10 0.010 0.25 A2 IN. MM 0.048 1.24 0.062 1.57 b IN. MM 0.012 0.30 0.020 0.50 C IN MM 0.007 0.17 0.011 0.28 D IN. MM 0.386 9.80 0.393 9.98 e IN. MM
0.050 BSC
1.27 BSC
E1 IN. MM 0.150 3.81 0.158 4.01 H IN. MM 0.230 5.84 0.244 6.20 L IN. MM 0.016 0.40 0.050 0.89 Θ 0° 8°
DS2105S SCSI TERMINATOR 16–PIN SOIC (300 MIL) The chamfer on the body is optional. If it is not present, a terminal 1 identifier must be positioned so that 1/2 or more of its area is contained in the hatched zone. PKG 16–PIN DIM MIN MAX A IN. MM 0.094 2.38 0.105 2.68 A1 IN. MM 0.004 0.102 0.012 0.30 A2 IN. MM 0.089 2.26 0.095 2.41 b IN. MM 0.013 0.33 0.020 0.51 C IN MM 0.009 0.229 0.013 0.33 D IN. MM 0.398 10.11 0.412 10.46 e IN. MM E1 IN. MM 0.290 7.37 0.300 7.62 H IN MM 0.398 10.11 0.416 10.57 L IN MM 0.016 0.40 0.040 1.02 Θ 0° 8°